In this study, a detailed analysis of the influences of cavitation nose structure of a high-speed projectile on the trajectory stability during the water-entry process was investigated numerically. The Zwart-Gerber-Belamri (Z-G-B) cavitation model and the Shear Stress Ttransport (SST)k-ω turbulence model based on the Reynolds Averaged Navier–Stokes (RANS) method were employed. The numerical methodology was validated by comparing the numerical simulation results with the experimental photograph of cavitation shape and the experimental underwater velocity. Based on the numerical methodology, the disk and the conical cavitation noses were selected to investigate the water-entry characteristics. The influences of cavitation nose angle and cavitation nose diameter of the projectile on the trajectory stability and flow characteristics were carried out in detail. The variation features of projectile trajectory, velocity attenuation and drag were conducted, respectively. In addition, the cavitation characteristics of water-entry is presented and analyzed. Results show that the trajectory stability can be improved by increasing the cavitation nose angle, but the drag reduction performance will be reduced simultaneously. Additionally, due to the weakening of drag reduction performance, the lower velocity of the projectile will cause the damage of the cavitation shape and the trajectory instability. Furthermore, the conical cavitation nose has preferable trajectory stability and drag reduction performance than the disk cavitation nose.

It is crucial for the water-entry stability and safety of the polar ocean equipment to study the process of the cylinder entering the water and passing through ice holes. In this study, based on the volume of fluid model and Schnerr–Sauer cavitation model, the influences of the ice-hole constraint on the cavity evolution process, the flow field characteristics, and the motion characteristics of the oblique water-entry process of the cylinder under different ice-hole diameter conditions are investigated numerically. The numerical method is verified. Results show that the influence of the ice-hole constraint on cavity evolution is mainly reflected in three aspects: surface splash, cavity wall, and cavity surface closure time. The ice-hole constraint changes the flow range of the water near the free surface, affecting the direction and shape of the surface splashing. The ice-hole inhibits the cavity expansion near the free surface. Under the smaller ice-hole diameter condition, the left-sided cavity wall directly collides with the inner wall of the ice-hole, which causes the curvilinearity of the left wall of the cavity near the free surface. Simultaneously, under the ice-hole condition, the surface closure time of the cavity is altered, and the distribution of the air and vapor inside the cavity is changed. A larger shear deformation region appears near the free surface, and there are more large-scale vortices inside the cavity, which leads to the acceleration of the velocity of the fluid and the decrease in the pressure near the free surface. Moreover, the impact force is changed at the initial stage of the cylinder passing through the ice-hole. The ice-hole condition leads to a faster velocity attenuation and a greater deflection during the oblique water-entry process of the cylinder.

To further understand a muzzle combustion mechanism in high-altitude firing, the influence of supersonic flow on a muzzle combustion phenomenon is investigated. The set of internal ballistic equations is employed, providing accurate velocity and pressure when the projectile moves to the muzzle. Multispecies transport Navier–Stokes equations with complex chemical reactions are solved by coupling a real gas equation of state, the Soave–Redlich–Kwong model, and a detailed chemical reaction kinetic model. The development of muzzle flow with chemical reaction is simulated. The interaction of chemical reactions with the muzzle flow field is obtained by numerical simulation in order to explain the muzzle combustion phenomenon of fire at supersonic flight. The mechanism of muzzle combustion influenced by supersonic incoming flow is analyzed in detail. It is demonstrated from the results that the shock wave and the expansion of the jet are restrained so that the combustion is compressed behind the projectile, at the same time generating a second region of combustion behind the muzzle under the influence of supersonic incoming flow.

In this study, the tail-slapping behavior of an oblique water-entry projectile is investigated through high-speed photography technology. The experimental images and data are captured, extracted and processed using a digital image processing method. The experimental repeatability is verified. By examining the formation, development and collapse process of the projectile’s cavity, this study investigates the impact of the tail-slapping motion on the cavity’s evolution. Furthermore, it examines the distinctive characteristics of both the tail-slapping cavity and the original cavity at varying initial water-entry speeds. By analyzing the formation, development and collapse process of the cavity of the projectile, the influence of the tail-slapping motion on the cavity evolution is explored. Furthermore, it examines the evolution characteristics of both the tail-slapping cavity and the original cavity under different initial water-entry speeds. The results indicate that a tail-slapping cavity is formed during the reciprocating motion of the projectile. The tail-slapping cavity fits closely with the original cavity and is finally pulled off from the surface of the original cavity to collapse. In addition, as the initial water-entry speed increases, both the maximum cross-section size of the tail-slapping cavity and the length of the original cavity gradually increase. With the increase in the number of tail-slapping motions, the speed attenuation amplitude of the projectile increases during each tail-slapping motion, the time interval between two tail-slapping motions is gradually shortened, the energy loss of the projectile correspondingly enlarges, and the speed storage capacity of the projectile decreases.

A two-way fluid–structure interaction (FSI) method for the water-entry process of a structure colliding with the floating ice is established. The two-way FSI method is validated by a collision experiment between an ice floe and a cylinder. Subsequently, the cavity evolution, hydrodynamic load, and motion characteristics during the water-entry process of the structure colliding with the floating ice are investigated. In addition, the influence of different distances between the axis of the structure and the edge of the floating ice on the water-entry characteristics is conducted. The results show that after the collision, the outward flipping motion of the floating ice forms the floating ice cavity, promotes the expansion of the structure cavity, and delays the closure time of the cavity, resulting in a significant increase in the size of the structure cavity compared to the ice-free environment; the effect is further exacerbated by an increase in the distance between the structure and the floating ice. Moreover, under the floating ice environment, the fluctuation and amplitude of the hydrodynamic load on the structure and the total horizontal displacement of the structure are reduced. The interaction force generated by the collision between the structure and floating ice becomes the main reason affecting the motion trajectory. As a result of the collision with the floating ice, the velocity attenuation is faster than that under the ice-free environment.